A stem cell line is a family of constantly-dividing cells, the product of a single parent group of stem cells. Stem cells are typically undifferentiated cells that are obtained from human or animal tissues and can replicate for long periods of time in vitro. Embryonic stem cells (ES cells) are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst.
ES cells are of particular interest because they are pluripotent, meaning that they are able to differentiate into all derivatives of the three primary germ layers: ectoderm, endoderm, and mesoderm. When stem cells are provided with the right conditions (i.e., when provided with the right mix of co-factors and no stimuli for differentiation), ES cells can maintain their pluripotency through multiple cell divisions.
Human ES cells are typically grown on a layer of so-called “feeder cells.” One example of feeder cells that are typically used are mouse embryonic fibroblasts (MEFs). MEFs adhere to the ES cells and provide enzymes, nutrients, growth factors, and other cofactors that help to maintain the human ES cells in their undifferentiated state. Without the proper culture conditions, embryonic stem cells will rapidly differentiate.
While feeder cells can be usefully employed for culturing stem cells, the stem cells typically need to be separated from the feeder cells before they can be used for implantation or other subsequent work. Current techniques (e.g., enzyme peeling or colony cutting) are labor intensive and difficult. Moreover, incomplete separation of the stem cells from the feeder cells can lead contamination of the cultured stem cells, rendering them unusable for many applications.